Dear statalisters, can someone help me out with this basic question?
I need to calculate the probability of the following event:
That at least one patient out of 99 suffers from kidneycancer
(incidence 15/100000 pr year) over a time period of 15 years.

Sounds like a good exam question. I think it is easier to figure out
the probability that no one gets kidney cancer. The probability of
one person not getting kidney cancer in a year is 1 -
15/100000. The probability of one person not getting kidney cancer
over 15 years is (1 - 15/100000)^15. The probability that 99 people
will be so lucky is (1 - 15/100000 )^15^99:

. di (1 - 15/100000 )^15^99
.80030153

So, the probability that at least 1 gets kidney cancer is

. di 1 - ((1 - 15/100000 )^15^99)
.19969847

So, there is about a 20% chance at least one person gets kidney cancer.